Patients with mastocytosis are more likely to develop significant liver pathology if they have category II disease (mastocytosis with an associated hematologic disorder) or category III disease aggressive mastocytosis). Liver pathology includes mast cell hyperplasia and fibrosis, sometimes leading to portal hypertension. Patients with category I disease (indolent mastocytosis) are less likely to develop these problems. Liver-spleen scans were of value in assessing liver size, and in identifying other types of problems such as liver hemangiomas. Based on these findings routine liver biopsy is not recommended in the evaluation of mastocytosis. Liver biopsy should only be performed on patients with laboratory and scan evidence of significant liver disease. Preliminary studies are underway to assess cytokine profiles in mastocytosis patients, with emphasis on stem cell factor. Suction blisters are raised over urticaria pigmentosa lesions which contain collections of mast cells. Blister fluid is assayed for cytokines appearing in blister fluid over several hours. It is hoped that this study will identify an abnormal cytokine profile associated with mast cell hyperplasia.